Field of Invention
The present invention relates to a mooring line restrainer for restricting the area on the deck of a ship of the snap-back zone of a snapped high tension mooring line in order to eliminate or at least reduce injury to ship's personnel and equipment. More particularly, the invention relates to development of novel structural frameworks which can be setup by positioning and linking the mooring line restrainers around the mooring lines on the deck of a ship for restraining any snapped mooring line to a much smaller area.
Description of Related Art
A Mooring refers to any permanent structure to which a vessel may be secured. A ship is secured to a mooring through mooring lines to forestall free movement of the ship on the water. An anchor mooring fixes a vessel's position relative to a point on the bottom of a waterway without connecting the vessel to shore. A Mooring Operation involves laying mooring lines to remote off board locations like anchors, quays, wharfs, tugs, other ships or mooring buoys for securing a ship in a given position.
It is, a known fact that snapping of lines constitutes one of the principal hazards associated with mooring operations. The lines can and do part occasionally. Numerous accidents, many of them fatal, have been regularly reported over the years. When lines under stress break suddenly, the “free end tends to ‘whip’ or ‘oscillate’ violently” and hit anybody or anything within their path with tremendous force. A snapped mooring line recoils in an area designated as the “Snap-back Zone”. Statistical evidence shows that in 53 percent of all cases of personal injuries arising from mooring incidents, ropes (wire or fibre) have parted under load and personnel within ‘snap-back zones’ have been hit. In 42 percent of cases, ropes/wires have not parted, but injuries have resulted from ropes jumping/slipping off drum-ends or bitts, or personnel being caught or ‘dragged’ by ropes, fixtures coming off mountings and from other causes [UK P&I Club's Loss Prevention Bulletin January 2009].
Qualified seafarers are aware of the fact that a snapback zone exists when a mooring line is under tension, and the mooring crew are expected to take this into account when they are working mooring lines on deck. It is possible to roughly estimate the limits of these ‘snap-back’ zones and if they are highlighted on the deck, the mooring crew can avoid standing inside or close to these danger areas. Painting these areas also helps supervising officers instruct crew to keep clear when lines are coming under tension. Highlighting mooring line snap-back zones ensures that crew can visibly see the danger areas without having to purposely think about them while working.
The shapes and limits of these danger zones have been roughly estimated, and as stated earlier as a precaution these are recommended to be marked on the deck, and the mooring crews are advised not to stand inside or close to these areas. But very often the mooring crew are required to lay more than one line within the area or because of some other operational considerations it may not be always practicable to avoid the snap-back zones. Mooring areas in many cases may also contain several trip and obstruction hazards, and highlighting these is a good starting point.
However, in several cases the number and arrangement of mooring lines can even create several overlapping snap-back zones, and it would be difficult for the mooring crew to avoid these dangerous areas. It is also widely recognized that the estimation of the exact size of these snap-back zones is a very complex analytical problem, and cannot be determined with any reasonable degree of assurance, and thus the mooring crew, is continuously exposed to danger.
Numerous accidents, many of them fatal, have involved seamen being caught in bights of or getting entangled with mooring ropes in motion and being dragged into mooring equipment or fittings. Mooring operations are hazardous, mainly because of the great loads the mooring lines are subjected to, which means that they are likely to part with little warning and great force. When a line breaks or is suddenly released under tension, it will travel back probably within a narrow cone around a straight line, striking anybody or anything in its path. If the line leads around a roller or a lead, then it may potentially whip around in a wider arc.
However, since it is known that the actual dimension of such areas is difficult to determine, and may potentially extend over an area larger than the limits normally shown in various official safety manuals. This is because there are too many factors like material, age/condition, and length of line deployed, the mode of failure, and the angle of line that influence the behavior of a snapped mooring line. Therefore, the dynamics of a snapped mooring line being very complex is not amenable for analysis by simple mathematical models. A snapped line behaves in a very unpredictable chaotic manner.
In view of this, the practice of reliance on the shape and size of the snap-back zones determined on the basis of unsound reasoning only provides limited safety in many situations. In reality the incorrectly marked snap-back zones may even provide a false sense of safety and security to the mooring crew.